The present invention relates to an electronical protective circuit in a device for reducing possible vibrations of a vehicle body due to rough idling of an engine of the vehicle.
Conventionally, in the field of automobile techniques, various techniques are proposed which concern a reduction in the vibrations of the vehicle body due to fluctuations of the engine torque. For example, in Unexamined Japanese Publication JP-B-62-31172 of Japanese Patent Application No. 57-68316 filed by Toyo Cogyo Co., Ltd. on Apr. 22, 1982, a technique is proposed which suppresses vibrations due to periodic fluctuations of the torque generated on the crankshaft synchronously with the combustion stroke of the engine. In this technique, a periodic increase in the torque of the combustion stroke of the engine is detected, a larger field current is caused to flow through the field coil of an alternator to increase the load torque on the alternator to thereby suppress an increase in the torque of the engine and hence reduce engine vibrations and vehicle body vibrations.
The vehicle body vibrations include periodic torque fluctuations due to intermittent combustion strokes of the engine as mentioned above as well as irregular combustion generated during idling to be described below.
Rough idling is likely to occur when the load changes rapidly, for example, when engine speed changes from high speed operation to idling in which case combustion is likely to become unstable and hence when combustion chamber pressure is not sufficient. The irregular combustion rapidly reduces the engine speed. Therefore, the engine is greatly swung in the direction in which the engine rotates around the output shaft (or in the rolling direction). Thus, if the engine is of vertical type like an FR (Front Engine Rear Drive) vehicle, engine vibrations are transmitted through the mount to the vehicle body to thereby cause abnormal vibrations. The body vibrations due to rough idling are different in generative mechanism from periodic vibrations due to engine combustion stroke as mentioned above and are generated irregularly, so that the device for suppressing periodic torque fluctuations of the engine mentioned above cannot eliminate such problems. Since the frequency of the vehicle body vibrations due to rough idling is low, for example, 5-8 Hz, reduction of the vibrations using a mechanical system of a dynamic damper is not practical because the very large-sized damper is required.
A circuit which generates a torque in the alternator body (stator) by increasing the field current in the alternator includes a combination of other electric circuits and elements and a voltage regulator for regular generation control, so that a protective circuit is required which maintains a normal generating function is required even when an abnormality is produced in those additional circuits.